The machinery manufacturing industry possesses a unique advantage in China. Joining the WTO has provided a great opportunity for Chinese-made products entering into the global markets, particularly the small universal gas engine which is powered by gaseous fuels such as natural gas, LPG or Biogas. The applications for engines with its capacity less than 19 kW have been developed rapidly. This type of engines are commonly used on portable devices such as small generator sets, high-pressure cleaner, lawn mower and water pumps, etc.
There are specific technical challenges on such applications. Firstly, the operating condition of the engine is subject to larger range of variations comparing to automotive engine whose operating condition is usually stable and predictable. Secondly, the fuel supply is usually in gaseous state (such as output from domestic LPG bottle or NG pipeline) rather than liquid state. The seal methods become more critical for gaseous mixer because the air/fuel ratio will be changed if air is sucked into the fuel passage or gas leaks out of the passages. The ambient temperature and gas supply pressure are subject to change from time to time, hence the metering method for controlling the amount of gas entering into the mixer is different from liquid fuel. The prior technology and control mechanism that were used on liquid fuel may not be suitable for such application (such as the mechanism described in U.S. Pat. No. 3,224,425). Thirdly, the engine is usually supplied as a general power unit to the third-parties such as the manufacturers of generator sets, high-pressure cleaner, lawn mower and water pump, etc. However, for different devices, the required engine characteristics of its torque or performance curve are different. Therefore, there is a need for some convenient ways for the engines to achieve different performance curve without significant structural changes to suit various applications. Further, due to the nature of the small size and the cost constraint, the advanced ECU-based control system is usually too expensive to be feasible on such applications.
Due to the nature of small universal gas engine, a specially-designed gaseous mixer is required to properly control the mixture ratio of air and gas according to different operating conditions. Currently the gaseous mixer for small universal gas engine usually consists of a mixer body, a choker, an air inlet port, a gas passage, a main metering jet, a mixture outlet port, a throttle valve, a main passage and an auxiliary passage. The air from the air inlet port is mixed with the gas coming from the main metering jet to form a combustible gaseous mixture. The performance of the gaseous mixer varies with the load of the engine and the concentration of the combustible gaseous mixture should vary accordingly. However, the present gaseous mixers only have one gas passage for fuel supply and thus the fuel amount cannot be adjusted according to the engine load. The inability of adjusting the gaseous mixture to the engine performance results in the improper work of engine. A common problem is that the gaseous mixture is too rich and thus causes an improper working condition for engine, such as difficulty to start up, fluctuation of rotary speed under idling or partial load conditions, flareback at mixer and back fire in exhaust pipe, etc.
The prior art, U.S. Pat. No. 322,445, disclosed a device structure for automatic adjustment of liquid fuel and air according to engine operating condition by means of a crank linkage device with structure extending outwardly through the wall of carburetor. Another prior art, U.S. Pat. No. 3,365,179, disclosed a carburetor of automatic adjustment in fuel and air and the secondary air valve is actuated by venturi or manifold pressure. Such control mechanism will not be functioning for gaseous engines and essentially different to the proposed invention.